The present invention relates to a method of and a device for processing the end of a pipe so as to form either a reduced or an expanded terminal portion. Particularly, this method or device is suited to a metal pipe, in which there is a danger of stresses being set up during the process, and of springing back of the end after processing.
Up until now, pipe end processing--that is, providing a reduced or an expanded terminal portion on a pipe--has been performed by applying a diameter changing element, like an expanding punch or a reducing die, to the end of the pipe. However, a problem has arisen, in that after this diameter changing element has been applied to the end of the pipe, and thereby the diameter of the end portion of the pipe has been modified, when the diameter changing element has been withdrawn from the end of the pipe, the elasticity of the material of the pipe has caused a spring-back effect, so that the diameter-changed end of the pipe has altered in size and form. Thus, an expanded end of a pipe has finally turned out to be smaller than desired, and a reduced end of a pipe has finally turned out to be larger than desired. Further, sometimes stresses have been set up in the diameter-changed end, due to cracks in the material thereof, and the like, and since these stresses are not properly relieved irregularities of the form of the pipe end often occur. For all these reasons, accurately formed pipe ends have not been properly formed, up till now.